Cell-Active Peptide Inhibitors of the FANCM-RMI Interaction

The FANCM-RMI protein–protein interaction plays
an essential
role in cancers that extend their telomeres through the Alternative
Lengthening of Telomeres (ALT) pathway. Here, we report the first
cell-active peptide inhibitors of FANCM-RMI. Screening of mRNA-displayed
peptide libraries treated with trans-1,4-dibromo-2-butene
led to the discovery of both linear and cyclic peptide hits that bind
RMI at the FANCM interaction site. The most potent peptides engage
RMI with nanomolar affinity (KD = 4–31
nM) and outcompete the native peptide mimic of FANCM (IC50 = 24–155 nM). A bound X-ray crystal structure of the top
hit revealed novel interactions at the RMI binding site that were
not found in the native interaction. Conjugation to a cell-penetrating
peptide resulted in inhibitors that induced an antiproliferative effect
in ALT-positive osteosarcoma cell lines. These inhibitors represent
the first bioactive RMI binders that can be used as chemical tools
for studying the involvement of FANCM-RMI in ALT-driven cancers.