Key Findings
- Purpose
Review preclinical and translational evidence for targeting β-chain Cysteine-93 (βCys93) as an allosteric regulator of hemoglobin affinity and as a potential antisickling strategy distinct from α-chain modulators (e.g., voxelotor). - Population / Evidence Base
Decades of in vitro experiments, animal/preclinical models, ex vivo human RBC work, and large cardiovascular pharmacogenomic studies of dalcetrapib (e.g., dal-OUTCOMES pharmacogenomic cohort). No clinical trials of βCys93-targeting agents in SCD patients have been reported. - Headline Result
Multiple thiol-reactive compounds (iodoacetamide, N-ethylmaleimide, isothiocyanates, RRx-001, triazole disulfides, glutathione derivatives, garlic-derived disulfides) demonstrate that βCys93 modulates Hb oxygen affinity and HbS polymerization in vitro. Among these, dalcetrapib, a lipophilic thio-ester with favorable oral pharmacology in cardiovascular trials, binds strongly to hemoglobin, partitions into RBCs in a saturable manner, reduces HbS polymerization in vitro, and improves RBC deformability. However, safety and efficacy in SCD remain untested. - Why It Matters
βCys93 is conserved and mechanistically linked to Hb allostery, nitric oxide bioactivity, and redox signaling; a clinically viable βCys93 modulator could offer an oral, complementary antisickling approach (distinct from existing α-chain drugs) and potentially improve RBC rheology and reduce sickling-related complications. Dalcetrapib’s existing safety database in cardiovascular populations and its pharmacogenomic signal in populations of African ancestry make it a pragmatic repositioning candidate. - Evidence Gaps
Critical gaps include the absence of in vivo SCD data, incomplete understanding of dalcetrapib’s RBC binding reversibility and functional impact in patients, limited safety data for chronic thiol-reactive exposure in SCD, potential off-target reactivity, and the need for translational studies linking RBC binding to clinical outcomes. Prospective SCD trials (with PK/PD, genotype stratification, and RBC functional endpoints) are required.
Source: Journal of Sickle Cell Disease – Challenges of the allosteric regulation of hemoglobin by interaction with Cys93 of the β chain for the treatment of sickle cell disease.
Regulatory & Guideline Watch
Dalcetrapib has been advanced in cardiovascular trials (phase-3 pharmacogenomic) but is not approved or studied for SCD; current ASH/NHLBI SCD guidelines do not address βCys93-targeted therapies. Any therapeutic repurposing would require SCD-specific safety and efficacy trials as well as regulatory submissions.