Discovery of Potent Coumarin-Based Kinetic Stabilizers of Amyloidogenic Immunoglobulin Light Chains Using Structure-Based Design

In
immunoglobulin light-chain (LC) amyloidosis, transient unfolding
or unfolding and proteolysis enable aggregation of LC proteins, causing
potentially fatal organ damage. A drug that kinetically stabilizes
LCs could suppress aggregation; however, LC sequences are variable
and have no natural ligands, hindering drug development efforts. We
previously identified high-throughput screening hits that bind to
a site at the interface between the two variable domains of the LC
homodimer. We hypothesized that extending the stabilizers beyond this
initially characterized binding site would improve affinity. Here,
using protease sensitivity assays, we identified stabilizers that
can be divided into four substructures. Some stabilizers exhibit nanomolar
EC50 values, a 3000-fold enhancement over the screening
hits. Crystal structures reveal a key π–π stacking
interaction with a conserved tyrosine residue that was not utilized
by the screening hits. These data provide a foundation for developing
LC stabilizers with improved binding selectivity and enhanced physicochemical
properties.