Discovery and Optimization of 5‑Hydroxy-Diclofenac toward a New Class of Ligands with Nanomolar Affinity for the CaMKIIα Hub Domain

The Ca2+/calmodulin-dependent
protein kinase II α
(CaMKIIα) is a brain-relevant kinase involved in long-term potentiation
and synaptic plasticity. We have recently pinpointed the CaMKIIα
hub domain as the long-sought-after high-affinity target of γ-hydroxybutyrate
ligands substantiated with a high-resolution cocrystal of 5-hydroxydiclofenac
(3). Herein, we employed in silico approaches
to rationalize and guide the synthesis and pharmacological characterization
of a new series of analogues circumventing chemical stability problems
associated with 3. The oxygen-bridged analogue 4d showed mid-nanomolar affinity and notable ligand-induced
stabilization effects toward the CaMKIIα hub oligomer. Importantly, 4d displayed superior chemical and metabolic stability over 3 by showing excellent chemical stability in phosphate-buffered
saline and high resistance to form reactive intermediates and subsequent
sulfur conjugates. Altogether, our study highlights 4d as a new CaMKIIα hub high-affinity ligand with enhanced pharmacokinetic
properties, representing a powerful tool compound for allosteric regulation
of kinase activity with subtype specificity.