Back to Annual Meeting

BACKGROUND: Infantile hemangiomas (IH) are the most common benign tumor of infancy and are thought to originate from hemangioma stem cells (HemSCs). While there are currently no FDA-approved treatments for IH, propranolol has been recently discovered to be an effective treatment for problematic hemangiomas. Propranolol is a pan- beta-adrenergic receptor antagonist, suggesting that the beta-adrenergic signaling pathway plays a role in IH pathology. We hypothesized that propranolol’s effects are preferentially mediated via the beta-1 and/or beta-2 adrenergic receptors in HemSCs.
METHODS: CD133+ HemSCs isolated from resected IH specimens were treated with beta-1 adrenergic receptor selective antagonist, atenolol, or beta-2 adrenergic receptor selective antagonist, ICI 118,551 (ICI), and compared to propranolol. Effects of beta-adrenergic blockade in HemSCs were assessed by proliferation assay using a WST-8 cell counting kit, and cytotoxicity assay using the fluorescence-based digital image microscopy system, DIMSCAN. Effects of beta-adrenergic blockade on downstream effectors cAMP and mitogen-activated protein kinase (MAPK) were assessed. cAMP levels after isoprenaline stimulation were measured using a LANCE Ultra cAMP kit. The presence of endogenous MAPK and activated phosphorylated MAPK-P were determined by immunoblotting, and quantified using Image J. Student’s t-test and Prism were used for statistical analysis.
RESULTS: ICI treatment resulted in a dose-dependent decrease in HemSC proliferation, similar to propranolol (p<0.005; Figure 1A), while atenolol treatment did not alter HemSC proliferation (Figure 1B). Cytotoxicity results showed propranolol and ICI with nearly identical potencies for HemSCs (LC50=159uM and 169uM, respectively), while HemSCs were resistant to atenolol (Figure 1C). Activation of beta-adrenergic signaling with isoprenaline elevated HemSC cAMP levels in a dose dependent manner (1961pM; Figure 2A), and was significantly inhibited by the presence of both propranolol (395pM; p<0.01) and ICI (399pM; p<0.01), but not atenolol (Figure 2B). MAPK activation was observed in the presence of both propranolol (15.5-fold) and ICI (19.5-fold), while atenolol had no effect (Figure 3).
CONCLUSIONS: The beta-2 selective antagonist ICI mirrored the effects of propranolol, as seen by reduced proliferation, increased cytotoxicity, cAMP blockade, and MAPK activation in HemSCs. The beta-1 selective antagonist atenolol had little effect. Thus, effectiveness of propranolol in treating IH may be mediated via the beta-2 adrenergic receptor pathway. The development and use of beta-2 selective antagonists for hemangiomas would minimize potential adverse effects from non-selective beta-adrenergic antagonists such as bradycardia and hypotension that has been associated with beta-1 inhibition.