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Recombinant immunoglobulin libraries of single chain molecules (sc) from the variable domains of antibody light and heavy chains (Fv), have great promise for new approaches to radioimmunotherapy (RIT). However, creating and evaluating scFv from diverse sources is time consuming and differences in molecular format can influence in vitro and in vivo characteristics. Furthermore, scFv do not have optimal characteristics for targeting therapy to tumor because of their small size and univalent binding. Diabody molecules at least twice the size of scFv are better for RIT because bivalent and bispecific molecules can be constructed. A polymerase chain reaction (PCR) based primer system was created to easily convert scFv genes into a diabody gene format, once they have been placed into pCANTAB 5E, a readily available vector. The primer system for this diabody gene platform was developed and tested by constructing an anti-lymphoma/anti-chelate, bispecific diabody (anti-HLA-DR/anti-DOTA). Two mouse scFv libraries were screened for reactive clones using recombinant phage display techniques. Selected mouse anti-HLA-DR and anti-DOTA scFv genes were combined, ligated into the pCANTAB 5E vector that co-expressed these self-assembling scFv in E. coli as two mismatched nonlinked pairs (VHA-link-VLB; VHB-link-VLA). The diabody protein that was purified from periplasm had the expected molecular characteristics when analyzed by sequencing, chromatography, electrophoresis and Western blot. This modular gene design platform provides methodology for easy and rapid creation of diabody molecules from diverse scFv libraries. Diabodies from various scFv can easily be produced, thereby facilitating comparative preclinical studies en route to development of new tumor targeting molecules.

Pretargeting techniques have shown promise for enhancement of the therapeutic index of radioimmunotherapy for cancer. However, methods to vary and compare antibody configurations and select optimal combinations have proved rather formidable. New options for the construction of pretargeting molecules are provided by sophisticated use of the diversity and malleability of antibody genes. Diverse arrays of single-chain antibody fragments (scFvs) can now be obtained reactive with virtually any target antigen by selection from human naive phage antibody libraries. ScFvs can also be cloned directly from hybridoma for construction of phage libraries that facilitate subsequent manipulation: e.g., affinity maturation and modification of specificity. ScFvs affinity selected from these sources to their specific antigen targets have demonstrated a wide spectrum of binding characteristics. ScFvs selected from a large human naive phage antibody library by binding Cu-1,4,8,11-tetra-azacyclotetradecane-N,N',N'',N'''-tetraacetic acid (TETA) or Y-1,4,7,10-tetra-azacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) have shown diversity by DNA fingerprints. DNA sequence information confirmed that the anti-TETA scFv represented diverse scFv gene families. ScFvs for Y-DOTA and those for lymphoma-associated HLA DR10 (Lym-1) were selected in a similar manner from mouse antibody gene libraries derived from hybridoma. ScFv clones for each of these antigens were chosen for further study based on the results of ELISA assays involving the respective cell membrane or metal chelate antigens. A PCR primer system built to pCANTAB 5E expression vector sequence was designed to facilitate cloning of antibody heavy (V(H)) and light (V(L)) genes from selected scFvs as cassettes into diabody modules. Thus, chosen scFvs could be expressed in the same diabody format for comparative study. Selected mouse anti-DOTA scFv and Lym-1 scFv genes were linked as V(HA) anti-DOTA-link-V(LB) Lym-1; V(HB) anti-DOTA-link-V(LA) Lym-1 and ligated into the pCANTAB 5E vector. Corresponding diabodies were expressed in Escherichia coli and purified by affinity chromatography. Here we provide a perspective on the power of antibody phage libraries and the possibilities of creating simple molecular formats that can be used en route to the development of new tumor targeting and pretargeting molecules.

Monoclonal antibodies were raised against yttrium(III)-1, 4, 7, 10-tetraazacyclododecane-N,N',N''N'''--tetraacetic acid (Y-DOTA) and copper(II)-1, 4, 8, 11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid (Cu-TETA). Four hybridomas with high Y-DOTA binding activity and one hybridoma with Cu-TETA activity were selected. MAbs were purified from mouse ascites by Protein A affinity chromatography and characterized. Affinity constants were determined by equilibrium dialysis and the highest affinity Y-DOTA MAb (K(aff) = 1.9 x 10(8) M(-1)) was further characterized by competitive ELISA. Gd-DOTA competed as well as Y-DOTA, whereas In-DOTA required 740x higher concentrations for 50% inhibition of this Y-DOTA MAb binding to human serum albumin-Y-DOTA-coated microtiter plates. These anti-metal chelate MAbs have potential use as vehicles for the pretargeted delivery of radiometal chelates to tumors.

Synergistic multimodality therapy is needed for breast cancer. Breast cancer frequently has p53 mutations that result in cells less likely to undergo apoptosis when exposed to DNA damaging therapies. Taxol (paclitaxel) is more effective in the presence of mutant p53. (90)Y-labeled DOTA-peptide-ChL6 ((90)Y-ChL6, where ChL6 is chimeric L6 antibody and DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid) is a novel radioimmunoconjugate for targeting radiation to cancer. It has a stable metal chelator and a peptide linker that can be catabolized by hepatic lysozymes. This study was designed to assess potential synergism between Taxol and (90)Y-ChL6 in a highly anaplastic breast cancer model, HBT 3477. There was no tumor response in mice receiving ChL6 or Taxol alone. In mice receiving (90)Y-ChL6 alone, 79% (15 of 19) of tumors responded although none were cured. If Taxol was administered 24-72 hours before (90)Y-ChL6, again, 79% (23 of 29) of tumors responded but 21% were cured. When Taxol was administered 6 or 24 hours after (90)Y-ChL6, 100% (46 of 46) of tumors responded and 48% were cured. Taxol given with (90)Y-ChL6 did not substantially increase toxicity. Enhancement of the therapeutic effect when Taxol was added to (90)Y-ChL6 therapy for HBT 3477 xenografts was striking. The synergistic therapeutic effect of Taxol with (90)Y-ChL6 may relate to the p53 mutant status and BCL2 expression in HBT 3477 cells, observations that increase the likelihood that the results of this study are relevant to therapy for breast cancer in patients. In conclusion, Taxol seemed to be synergistic with (90)Y-ChL6 in this human breast cancer model. Up to 50% of these anaplastic breast cancer xenografts were cured by combined modality therapy.