Phage library-derived human anti-TETA and anti-DOTA ScFv for pretargeting RIT

Pretargeting techniques have promise for radioimmunotherapy (RIT) in cancer because of the potential for markedly increasing the therapeutic ratio. Human antibody fragments can be retrieved from phage libraries and used to realize this potential. The library can be used to select the genetic material required to generate molecules with binding sites for both radiochelates and tumor antigens, In this study, human anti-chelate scFvs (single-chain fragments) for two metal chelates (Cu-TETA and Y-DOTA) were selected from a large, naive human scFv library. These anti-chelate scFvs were intended to serve as one arm of bispecific pretargeting molecules and to bind radiochelates given subsequently as Cu-67-TETA or Y-90-DOTA, Phage that displayed the anti-chelate scFv were selected by absorption to antibody (Lym-1) bound Cu-TETA or Y-DOTA, Enzyme-linked immunosorbent assays (ELISA) were performed to assess the intensity and specificity of phage binding to the specific chelate, Ninety-six clones demonstrating metal chelate binding seven times greater than to Lym-1 alone were chosen for diversity analysis. BstN I restriction digests were performed on DNA from these clones. Twenty-three and 43 different DNA fingerprint patterns were identified for anti-TETA and anti-DOTA clones, respectively, DNA sequencing of 39 anti-TETA clones for 23 different BstN I fingerprint patterns revealed 22 distinct sequences. Eleven of the anti-TETA clones were selected for further study. Five hundred to 1000 mu g (100 to 320 mu g per liter of culture) of purified scFv was produced from each of the 11 anti-TETA clones. Preliminary studies by BIAcore demonstrated evidence of 25- to 200-nM affinities. Comparable examination of the anti-DOTA clones is in progress, This study provides evidence that human scFv against unique synthetic targets can be readily selected from a large, naive human immunoglobulin phage library. Selections against metal chelated antibodies provided a wealth of scFvs with diverse binding affinities useful for engineering molecules for pretargeting RIT.