Site-directed chemical modification and crosslinking of a monoclonal antibody using equilibrium transfer alkylating crosslink reagents

A new, more reactive group of protein cross-linkers in the class of equilibrium transfer alkylating cross-link (ETAC) reagents has been synthesized. These compounds include alpha,alpha-bis[(p-chlorophenyl)methyl]- and alpha,alpha-bis[(p-tolylsulfonyl)methyl]acetophenones substituted in the acetophenone ring with chloro, nitro, amino, and carboxyl groups and derivatives. Included are an 125I-labeled ETAC reagent and a 111In-labeled DTPA (diethylenetriaminepentaacetic acid) ETAC for site direction and biodistribution studies. These ETAC compounds were reacted with unreduced and partially reduced antibody under mild pH (pH 4-8) and room temperature conditions to give cross-linked structures. Examination of resultant cross-linked antibody via size-exclusion HPLC, sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, and an enzyme linked immunosorbent assay revealed that (1) both interantibody as well as intraantibody cross-linking had occurred; (2) the level of inter- and intraantibody cross-linking varied with the substituent on the ETAC; (3) the stability of the cross-links on the reducing SDS gels varied with substituents on the ETAC; (4) little if any immunoreactivity was lost after reaction with one of the more effective ETAC cross-linking compounds; (5) the 125I-labeled ETAC sulfhydryl cross-linking in partially reduced antibody increased with pH whereas amine cross-linking with the unreduced antibody decreased with pH; (6) the optimum pH for sulfhydryl site direction was pH 5.0; (7) the 111In DTPA ETAC labeled antibody had a biodistribution in CD1 mice similar to that of the 111In bis cyclic anhydride DTPA labeled antibody.