Abstract P319: Eliminating Cardiotoxicity In Alpha1-adrenergic Receptor Antagonists

Abstract

Introduction: Alpha-1 adrenergic receptor (α1-AR) antagonists (α1-blockers) are efficacious antihypertensives, but ALLHAT found that doxazosin (Dzn) doubled the risk of heart failure (HF). We previously demonstrated that α1-ARs, specifically the α1A-AR, protect the heart, explaining the worse outcomes with Dzn in ALLHAT. Interestingly, α1-ARs localize to and signal at the nucleus in cardiac myocytes (CM), whereas α1-ARs localize to the sarcolemma in smooth muscle (SM). Hypothesis: We hypothesize that a membrane impermeant α1-blocker would inhibit α1-ARs in SM, reducing blood pressure, but preserve protective α1-signaling in CMs, preventing HF. Methods: We developed an α1A-AR homology model to define the structural basis of α1-blocker binding and modified existing α1-blocker structure to reduce cardiotoxicity. Using this model, we designed 30 compounds, synthesized 9 in gram quantities, and tested 2 compounds. Results and Conclusions: Binding assays identified 2 novel high affinity α1-ligands; α1705 (IC50 = 5.2 [CI:3.5,7.6] nM, n=3) and α1707 (5.8 [CI:4.2,8.1] nM, n=3) (Dzn: 7.7 [CI:6.3,9.2] nM, n=6). Uptake assays in cultured CM indicated uptake of Prazosin (10 μM Prz: 230 nM in CMs detected by mass spectrometry), whereas α1705 and α1707 were not detected. In HEK cells expressing α1A-AR at the cell surface, Prz, α1705, and α1707 (all 2 μM) inhibited Ca2+ transients (90%, 76%, 88%) induced by the α1A agonist A61603 (20 μM). In CM, A61603 increased ERK phosphorylation (1.55±0.04 fold, n=7, P<0.0001), a survival signal, which was blocked by Prz (1.21±0.06 fold, n=7, P=NS), but not α1705 (1.72±0.13 fold, n=7, P<0.001). Further, A61603 (20 μM) inhibited H202-induced CM death (-17.4±7.6%, n=5), which was reversed by Prz (30.9±15.4%, n=5, P=0.035), but not α1705 (-0.94±11.6%, n=5, P=NS). In DOCA-salt hypertensive mice, infusion of Prz or α1705 (2 mg/kg/d, 3 d) lowered systolic pressure (Cont: +18.9 mmHg, n=1; Prz: 6.4±3.2 mmHg, n=3, α1705: -6.1±5.6 mmHg, n=3), and while Prz was detected in CMs following 4 d, α1705 was not. In conclusion, we have developed a novel membrane impermeant α1-blocker with reduced cardiotoxicity that could improve hypertension outcomes, especially in patients suffering from chronic kidney disease or benign prostatic hyperplasia.