The β‐blockers carvedilol and nebivolol inhibit neoplastic transformation through a β2‐adrenergic receptor independent mechanism

Abstract

β‐adrenergic receptors (β‐ARs) are crucial mediators of physiological responses to catecholamines (i.e. epinephrine and norepinephrine), and β‐blockers competitively inhibiting β‐ARs thereby preventing the associated cardiovascular effects of β‐ARs. Aside from their cardiovascular function, β‐blockers are potential chemopreventive agents. Previous studies identified a subset of β‐blockers as potential cancer preventive agents. Carvedilol and nebivolol inhibit EGF‐induced neoplastic transformation of JB6 P+ cells, a non‐cancerous but transformation sensitive murine epidermal cell line. However, the antineoplastic mechanism(s) of action have yet to be elucidated. Therefore, we sought to evaluate the role of the β2‐AR, the only β‐AR present in JB6 P+ cells, in the β‐blocker antineoplastic effect. First, an EGF‐mediated soft agar transformation assay was utilized to evaluate the combined effect of carvedilol with either CGP 12177 or nadolol; CGP 12177 and nadolol lack a cancer preventive effect. 10 μM CGP 12177 (KD= −9.39) had no effect on carvedilol (KD= −9.40) mediated inhibition of EGF‐induced transformation of JB6 P+ cells: −6.48±0.09 IC50 versus −6.67±0.05 IC50 for carvedilol and carvedilol plus CGP 12177, respectively. Similarly, carvedilol combined with 10 μM nadolol (KD= −8.60) resulted in no shift in the concentration‐response curve (−6.55±0.03 IC50 versus −6.50±0.06 IC50). Since carvedilol is a non‐selective β‐AR and α1‐AR antagonist, we assessed the involvement of the α1‐AR by combining the β‐blocker nebivolol, that lacks α1‐AR activity, with 10 μM CGP 12177. Combination of nebivolol (KD= −7.91 for the β2‐AR) and CGP 12177 did not alter the potency of nebivolol (−6.46±0.11 and −6.81±0.12 for nebivolol and nebivolol plus CGP 12177, respectively). To further the pharmacological studies, the efficacy and potency of carvedilol in preventing EGF‐induced transformation of JB6 P+ cells was compared in scramble control shRNA and Adrb2 (β2‐AR) shRNA infected cells. With 72% β2‐AR knockdown, carvedilol prevented EGF‐mediated transformation of JB6 P+ cells (IC50= −6.02±0.07), although with a slightly reduced potency compared to the scramble control (IC50= −6.24±0.06). The data demonstrate that the β‐blocker carvedilol and likely nebivolol function as a cancer preventive agent independently of their widely‐understood action as β‐AR blockers.