Repurposing Tyrosine Kinase Inhibitors for Sickle Cell Disease: Focus on Band 3 Phosphorylation.

Sickle cell disease (SCD) is an autosomal recessive hemoglobin disorder that is mainly characterized by the presence of hemoglobin S (HbS; point mutation [Glu6Val] in the beta-globin gene). Under deoxygenated conditions, HbS polymerizes and serves as the primary trigger of oxidative stress in red blood cells (RBCs), promoting polymerization of Band 3, a major membrane scaffold protein that links the lipid bilayer to the spectrin-ankyrin cytoskeletal network. Phosphorylation at key residues within the cytosolic domain of Band 3 induces conformational changes that weaken ankyrin binding and enhance lateral mobility and clustering of Band 3. These effects are mediated through a coordinated network of erythrocyte tyrosine kinases, primarily spleen tyrosine kinase (SYK) and sarcoma (Src) family kinases, which act sequentially to modify distinct tyrosine residues. Structural features of these kinases, including tandem SH2 domains in SYK and conserved SH2-SH3-kinase domain architecture of Src family members, enable precise recognition of phosphotyrosine motifs and propagation of phosphorylation cascades. Sequence alignment and structural superimposition of SH2 domains across studied kinases demonstrate a highly conserved fold that is critical for phosphotyrosine recognition, suggesting potential overlap in substrate engagement. Therapeutically, targeting these kinases has shown considerable promise, as tyrosine kinase inhibitors (TKIs) reduce Band 3 phosphorylation, restore RBC deformability, and decrease hemolysis and vaso-occlusive interactions in vitro. Thus, in this narrative review, we focus on the regulation of Band 3 by the above-mentioned tyrosine kinases, as well as the therapeutic potential of TKIs in SCD.