Haplotype Targeting in Heart Failure Using a Biased Ligand β-blocker

BackgroundADRB1 and ADRB2, encoding cardiac myocyte {beta}1- and {beta}2-adrenergic receptors (ARs) that mediate pathologic myocardial remodeling in response to chronically increased signaling, contain N-terminus haplotype variants capable of influencing agonist- or biased ligand-induced receptor internalization that uncouples canonical signaling and initiates EGFR/ERK1/2 cardioprotection. MethodsIn two heart failure (HF) clinical trial genetic substudies we investigated effects of internalizing vs. internalization-resistant DRB1/ADRB2 haplotypes on clinical or biomarker responses to the biased ligand {beta}-blocker bucindolol vs. placebo or vs. the nonbiased {beta}1-antagonist metoprolol, and in haplotyped isolated human heart preparations we measured ERK1/2 activation in response to these same interventions. ResultsIn subjects with [&ge;]3 internalizing ADRB1+ADRB2 haplotypes (6.7% subcohort) placebo treatment was associated with fewer clinical events compared to subjects with internalization-resistant haplotypes (Odds Ratio (OR) 0.28, 95% CI (0.10, 0.82)). In contrast, placebo treatment in subjects with [&ge;]3 internalization-resistant haplotypes (70% subcohort) was associated with more clinical events in comparison to subjects with internalizing haplotype counterparts (OR 1.64 (1.46, 1.84)). Bucindolol treatment was equal to placebo in the [&ge;]3 internalizing subcohort, but was superior to placebo in the internalization-resistant subcohort (bucindolol vs. placebo OR 0.49 (0.41, 0.58)). In subjects with all 4 haplotypes internalization-resistant (25% subcohort), bucindolol vs. placebo reduced time to first event rates by 62.3{+/-}17.5% (P <0.01, 1.68{+/-}0.34 fold > the all-haplotypes parent population and additive to 1.92{+/-}0.58 fold when the ADRB1 haplotype contained Arg389 rather than Gly389). The same bucindolol vs. placebo pattern was observed for NT-proBNP or norepinephrine reduction vs. metoprolol. In these comparisons ADRB2 and ADRB1 haplotypes behaved similarly, and although the haplotypes differed in frequency between Black and non-Black subjects, within haplotypes there were no by-race differences in therapeutic effects. Bucindolol but not metoprolol activated ERK1/2 signaling in isolated ventricular preparations with [&ge;]3 internalization-resistant haplotypes. Conclusions1) Both {beta}1- and {beta}2-AR haplotypes regulate therapeutic responses in HF; internalizing species confer protection against clinical events in placebo-treated subjects, while in internalization-resistant haplotypes the biased ligand {beta}-blocker bucindolol but not the non-biased ligand metoprolol is associated with favorable effects. 2) The biased ligand cardioprotective effect may be related to internalization-dependent or -independent ERK1/2 activation.