A Priori Design, Combinatorial Synthesis, and Assessment of an Antipackaging Peptide Against Human Immunodeficiency Virus 1: Functional Role of Unnatural Trp Mimetics and Serendipitous Discovery of a Protease Inhibitor.

HIV-1 is a prevalent disease worldwide. While current therapies keep the virus at bay-suppressing viral loads and minimizing risks of transmission-viral mutations that confer drug resistance are still a significant problem. It would, therefore, be advantageous to have therapies that address viral targets that are highly conserved and critical for viral replication. One such option is ψRNA. This region of RNA serves as the recognition site for the NCp7 viral protein. The binding of NCp7 to ψRNA guides the packaging of intact viral RNA into nascent daughter virions. Thwarting this process leads to virions that incorporate nonfunctional RNAs and are not infectious. Based on prior studies, we designed, synthesized, and tested a library of nonproteinogenic tetrapeptides to target stem-loop elements of ψRNA known to interact with NCp7. Peptides incorporating aza-indole (tryptophan-like) amino acids displayed considerable anti-HIV and trophic-specific activity yet failed to inhibit packaging. Instead, our best analog (IC50 2.84 µM) was a potent protease inhibitor, comparable to FDA-approved Lopinavir (1.44 µM) and Nelfinavir (1.54 µM). Together, our studies demonstrate the perils that can accompany early-phase discovery efforts, and the serendipitous findings that can sometimes result. They also showcase the power of unnatural tryptophan mimics to imbue unique antiretroviral structure-activity.