Selection of muscle-binding peptides from context-specific peptide-presenting phage libraries for adenoviral vector targeting.

Production of cell-targeting vectors in part involves the addition of new targeting ligands to the vector to mediate binding to the cells of interest. For viral vectors, the ideal approach is to genetically engineer new ligands into the capsid proteins of the virus to generate a single agent to mediate therapy. Although this is ideal, this insertion of an exogenous ligand from one structural context into the differing structural context of a capsid protein can ablate the function of the ligand or disrupt viral assembly and function. To address this context problem for adenoviral vectors, we have engineered a "context-specific" peptide-presenting phage library. We have displayed a 12-amino-acid (12-mer) random peptide library between the H and I sheets of the fiber protein of adenovirus type 5 on the pIII protein of fd bacteriophage. This library was used for peptide selection against C2C12 mouse skeletal muscle cells. Five rounds of selection combined with four rounds of clearing on nontarget cells selected one primary peptide designated 12.51, which bound target C2C12 cells approximately 100-fold better than the positive control RGD peptide. Translation of 12.51 back into the fiber protein produced a ligand-modified adenoviral vector that mediated 14-fold-better transduction of target C2C12 cells. These data suggest context-specific peptide-presenting libraries may allow selection of compatible peptide ligands for functional translation into viral vectors for retargeting.