RESUMEN
Recombinant single-chain fragment variable (scFv) antibodies with specificity to tumor antigens can be used to target tumors in vivo. The approach to use administration of complexes of idiotypic-anti-idiotypic scFvs when targeting tumors has not been tested earlier, and from a theoretical point it could contribute to longer in vivo circulation and improved targeting efficiency by dissociation, when in contact with the target antigen. In this study two models to evaluate the targeting efficiency of such complexes were used. HeLa HEp-2 tumor cells were grown as multicellular tumor spheroids (MCTS) and exposed to the antibody constructs in vitro. The behavior in vivo was tested in an in vivo tumor xenograft model. To increase the size of the anticytokeratin 8 scFv, TS1-218, complexes were formed between TS1-218 and its anti-idiotype, alphaTS1 scFv. The functionality of (125)I-labeled TS1-218 alone and in complex was studied in both models. The uptake patterns were similar in both models. The idiotypic TS1-218 was able to localize to the MCTS and xenografted tumors, both alone and in complex with alphaTS1 scFv. TS1-218 in complex, however, demonstrated a significantly higher uptake than the monomeric TS1-218 in both models (p < 0.0005 and p < 0.0089, respectively). When complexes were administered in vivo, a slower clearance and an increased tumor half-life could be observed. The present investigation indicates that administration of targeting antibodies, with initially blocked antigen-binding sites by complex formation with their anti-idiotypes, may improve targeting efficiency.
