Differential effects of propranolol enantiomers on haemangioma-derived endothelial spheroids

Infantile Haemangioma, a vascular tumour in infants, is characterised by rapid vasculogenesis and proliferation followed by gradual regression. Ulcerations and disfiguring complications are common with the racemic mixture of propranolol, a β-blocker as the standard treatment for IH; however, the mechanism of action is not clearly defined. In this study, we have investigated the anti-angiogenic efficacy of propranolol and its enantiomers. Using an integrated approach combining 3D spheroid assays, quantitative mRNA and protein expression analyses along with mass spectrometry-based proteomics, the molecular and functional effects of each propranolol enantiomer were characterised using our novel 3D in vitro model of haemangioma endothelial spheroids. R-propranolol suppressed angiogenic factors and cytokines with less cytotoxicity compared to S-propranolol or the mixture. Proteomic profiling of R-propranolol treated spheres revealed downregulation of DNA repair pathways and enrichment of sphingolipid metabolism and CLEAR signalling pathway. Downstream molecular changes associated with these pathways were further evaluated by western blot and qPCR, which showed reduction in oxidative phosphorylation complexes II and III, and increase in HMGCR and SREBF1 after R-propranolol treatment. In summary, the angiogenic properties of R-propranolol, the potent isomer of the racemic mixture of propranolol were explored, which might have therapeutic implications for vascular anomalies involving pathological angiogenesis.