Phage display-based discovery of cyclic peptides against the broad spectrum bacterial anti-virulence target CsrA.

Small macrocyclic peptides are promising candidates for new anti-infective drugs. To date, such peptides have been poorly studied in the context of anti-virulence targets. Using phage display and a self-designed peptide library, we identified a cyclic heptapeptide that can bind the carbon storage regulator A (CsrA) from Yersinia pseudotuberculosis and displace bound RNA. This disulfide-bridged peptide, showed an IC50 value in the low micromolar range. Upon further characterization, cyclisation was found to be essential for its activity. To increase metabolic stability, a series of disulfide mimetics were designed and a redox-stable 1,4-disubstituted 1,2,3-triazole analogue displayed activity in the double-digit micromolar range. Further experiments revealed that this triazole peptidomimetic is also active against CsrA from Escherichia coli and RsmA from Pseudomonas aeruginosa. This study provides an ideal starting point for medicinal chemistry optimization of this macrocyclic peptide and might pave the way towards broad-acting virulence modulators.

Hit-to-lead optimization of a latency-associated nuclear antigen inhibitor against Kaposi's sarcoma-associated herpesvirus infections.

The Latency-associated nuclear antigen (LANA) plays a central role for the latent persistence of the Kaposi's Sarcoma Herpesvirus (KSHV) in the human host and helps to establish lifelong infections. Herein, we report our efforts towards hit-to-lead generation starting from a previously discovered LANA-DNA inhibitor. By tethering the viral genome to the host nucleosomes, LANA ensures the segregation and persistence of the viral DNA during mitosis. LANA is also required for the replication of the latent viral episome during the S phase of the cell cycle. We aim to inhibit the interaction between LANA and the viral genome to prevent the latent persistence of KSHV in the host organism. Medicinal chemistry-driven optimization studies and structure-activity-relationship investigation led to the discovery of an improved LANA inhibitor. The functional activity of our compounds was evaluated using a fluorescence polarization (FP)-based interaction inhibition assay and electrophoretic mobility shift assay (EMSA). Even though a crystal structure of the ligand protein complex was not available, we successfully conducted hit optimization toward a low micromolar protein-nucleic acid-interaction inhibitor. Additionally, we applied STD-NMR studies to corroborate target binding and to gain insights into the binding orientation of our most potent inhibitor, providing opportunities for further rational design of more efficient LANA-targeting anti KSHV agents in future studies.