Pindolol

The β1-adrenoceptor (β1AR) is a G protein-coupled receptor (GPCR) that is activated by the endogenous agonists adrenaline and noradrenaline. We have determined the structure of an ultra-thermostable β1AR mutant bound to the weak partial agonist cyanopindolol to 2.1 Å resolution. High-quality crystals (100 μm plates) were grown in lipidic cubic phase without the assistance of a T4 lysozyme or BRIL fusion in cytoplasmic loop 3, which is commonly employed for GPCR crystallisation. An intramembrane Na+ ion was identified co-ordinated to Asp872.50, Ser1283.39 and 3 water molecules, which is part of a more extensive network of water molecules in a cavity formed between transmembrane helices 1, 2, 3, 6 and 7. Remarkably, this water network and Na+ ion is highly conserved between β1AR and the adenosine A2A receptor (rmsd of 0.3 Å), despite an overall rmsd of 2.4 Å for all Cα atoms and only 23% amino acid identity in the transmembrane regions. The affinity of agonist binding and nanobody Nb80 binding to β1AR is unaffected by Na+ ions, but the stability of the receptor is decreased by 7.5°C in the absence of Na+. Mutation of amino acid side chains that are involved in the co-ordination of either Na+ or water molecules in the network decreases the stability of β1AR by 5-10°C. The data suggest that the intramembrane Na+ and associated water network stabilise the ligand-free state of β1AR, but still permits the receptor to form the activated state which involves the collapse of the Na+ binding pocket on agonist binding.

In this work, we examine methyl nuclear magnetic resonance (NMR) spectra of the methionine ε-[13CH3] labelled thermostabilized β1 adrenergic receptor from turkey in association with a variety of different effectors, including mini-Gs and nanobody 60 (Nb60), which have not been previously studied in complex with β1 adrenergic receptor (β1AR) by NMR. Complexes with pindolol and Nb60 induce highly similar inactive states of the receptor, closely resembling the resting state conformational ensemble. We show that, upon binding of mini-Gs or nanobody 80 (Nb80), large allosteric changes throughout the receptor take place. The conformation of tβ1AR stabilized by the native-like mini-Gs protein is highly similar to the conformation induced by the currently used surrogate Nb80. Interestingly, in both cases residual dynamics are present, which were not observed in the resting states. Finally, we reproduce a pharmaceutically relevant situation, where an antagonist abolishes the interaction of the receptor with the mini-G protein in a competitive manner, validating the functional integrity of our preparation. The presented system is therefore well suited for reproducing the individual steps of the activation cycle of a G protein-coupled receptor (GPCR) in vitro and serves as a basis for functional and pharmacological characterizations of more native-like systems in the future.

BackgroundS-pindolol has metabolic effects of potential benefit in cancer cachexia: reduced catabolism through nonselective β-blockade; increased anabolism through partial β2 receptor agonism; and increased appetite and reduced fatigue through central 5-hydroxytryptamine/serotonin receptor activity. A Phase 2a clinical trial demonstrated that S-pindolol can reverse weight loss and improve fat-free mass in patients with cancer-related weight loss. A comparative phase I bioavailability study of S-pindolol and racemic pindolol was performed to support the development of S-pindolol in cancer cachexia.MethodsThis two-part study assessed the comparative bioavailability and pharmacokinetics of single doses of S-pindolol benzoate (ACM-001.1) or pindolol (Part 1) and the steady-state pharmacokinetics and pharmacodynamics of multiple doses of ACM-001.1 and pindolol (Part 2) in healthy volunteers (NCT06028321). ACM-001.1 5, 10 and 15 mg and pindolol 15, 20 and 30 mg were tested. In Part 1, subjects were randomised to ACM-001.1 15 mg followed after a 48-h washout period by pindolol 30 mg, or the reverse sequence; another group received pindolol 15 mg. Subjects in Part 2 were randomised to pindolol 20 mg twice-daily or ACM-001.1 5, 10 or 15 mg twice-daily for 4 days. Bioavailability, pharmacokinetics, pharmacodynamics, potential for and extent of stereoconversion, and tolerability were assessed.ResultsParts 1 and 2 included 24 and 27 healthy volunteers, respectively. ACM-001.1 had predictable pharmacokinetics up to a dose of 15 mg twice daily, with low intersubject variability, after single and multiple doses (Tmax 1 vs. 1.5 h; Cmax 74 vs. 73.6 ng/mL; AUC(0-t) 440 vs. 414 ng·h/mL; t1/2 4.042 vs. 3.566 h). The bioavailability of S-pindolol after equivalent doses of pindolol (20 mg) and ACM-001.1 (10 mg) was comparable, and formal bioequivalence margins were met (90% CI for Cmax, AUC(0-t) and AUC(0-inf) within 80%-125% bioequivalence acceptance criteria). No evidence of stereoconversion of the S-enantiomer into the R-enantiomer, no accumulation, dose linearity and dose proportionality of S-pindolol over a range of doses were demonstrated; we also show indirectly that there was no food effect. ACM-001.1 was generally well tolerated, with no apparent relationship of side effects to dose, no serious adverse events, severe treatment-emergent adverse events (TEAEs) or deaths, and similar incidences of TEAEs (fatigue, dizziness, somnolence, nausea and headache) with ACM-001.1 10 and 15 mg and pindolol 20 mg.ConclusionsData from this bridging study of enantiomerically pure ACM-001.1 and its parent racemic drug, pindolol, support clinical trials of ACM-001.1 for the treatment of cancer cachexia.