Discovery of Potent and Selective Pyridone-Based Small Molecule Kinetic Stabilizers of Amyloidogenic Immunoglobulin Light Chains

Kinetic stabilization of amyloidogenic immunoglobulin light chains (LCs) through small molecule binding may become the first treatment for the proteinopathy component of light chain amyloidosis (AL). Kinetic stabilizers selectively bind to the native state over the misfolding transition state, slowing denaturation. Prior λ full-length LC dimer (FL LC₂) kinetic stabilizers exhibited considerable plasma protein binding. We hypothesized that the coumarin "aromatic core" of the stabilizers was responsible for the undesirable plasma protein binding. Here, we describe structure-activity relationship (SAR) data initially focused on replacing the coumarin aromatic core. 2-pyridones proved suitable replacements. We subsequently optimized the "anchor substructure" in the context of 2-pyridones, resulting in potent λ FL LC₂ kinetic stabilizers exhibiting reduced plasma protein binding. The 3-methyl- or 3-ethyl-3-phenylpyrrolidine-2-pyridone scaffold stabilized multiple AL patient-derived λ FL LC₂s in human plasma. This, coupled with X-ray crystallographic data, indicates that 3-alkyl-3-phenylpyrrolidine-2-pyridone-based stabilizers are promising candidates for treating the proteinopathy component of AL.