A Fully Synthetic “Phage-Like” System II: Synthesis and Live Cell Screening of Combinatorial Libraries of Peptides on Sub-cellular Sized Microspheres

Herein we present a new application of a recently demonstrated fully synthetic "phage-like" system for screening of combinatorial mixtures in a live cell assay. The new application includes the direct synthesis of peptides and combinatorial libraries on 2 µm cross-linked mono-dispersed microspheres bearing a panel of fluorescence tags. Their characterization using classical chemical analysis as well as biological recognition of the synthesized sequences on the microspheres by specific antibodies, demonstrate the robustness of the system. Two biased positional combinatorial peptide libraries derived from peptide DUP-1 were synthesized and screened for affinity to prostate cancer PC-3 cell line as compared to DUP-1, a peptide with good affinity for this cell line. The best sub-library was deconvoluted and mixtures of deconvoluted peptides on microspheres were screened for identifying the sequences with the best affinity for cells. The best peptide, DUP-1(1-12) 2 Ala with high affinity for PC-3 cells, was individually synthesized and validated in an independent binding assay. Finally, the cellular fate of DUP-1(1-12) 2 Ala in PC-3 cell line is demonstrated using confocal laser scanning microscopy. Overall, these results demonstrate that the synthetic phage-like system recently assessed for screening mixtures of small organic molecules, can be also used for synthesis and screening of combinatorial libraries of peptides in live cell assays.