Serotonin plays a key role in the development and maintenance of the pathobiology associated with pulmonary arterial hypertension (PAH). Plateletdriven and locally produced serotonin from lung tissue and arterial endothelial cells induce excessive growth of pulmonary artery smooth muscle cells. The unchecked growth of these cells is a major driver of PAH including the remodeling of pulmonary arteries that dramatically reduces the diameter and flexibility of the arterial lumen. Tryptophan hydroxylase 1 (TPH1) is the ratelimiting enzyme for biosynthesis of serotonin and is upregulated in PAH arterial endothelial cells, supporting TPH1 inhibition to treat PAH. Targeting the serotonin pathway via inhibition of peripheral serotonin and local production in diseased tissues, rather than individual receptor-mediated or receptorindependent mechanisms, may result in the ability to halt or reverse pulmonary vascular remodeling. Rodatristat ethyl, a prodrug for rodatristat, a potent, peripheral inhibitor of TPH1, has demonstrated efficacy in monocrotaline and SUGEN hypoxia nonclinical models of PAH and robust dose-dependent reductions of 5-hydroxyindoleacetic acid, the major metabolite of serotonin in plasma and urine of healthy human subjects. ELEVATE 2 (NCT04712669) is a Phase 2b, double-blind, multicenter trial where patients with PAH are randomized to placebo, 300 or 600 mg twice daily of rodatristat ethyl. The trial incorporates endpoints to generate essential clinical efficacy, safety, pharmacokinetic, and pharmacodynamic data needed to evaluate the ability of rodatristat ethyl to ameliorate PAH by halting or reversing pulmonary vascular remodeling through its unique mechanism of TPH1 inhibition. Herein we describe the experimental design highlighting the trial's unique features.
Morphine differs from most opiates for its poor ability to internalize μ opioid receptors (μORs). However, chronic treatment with morphine produces adaptational changes at the dynamin level, which enhance the efficiency of acute morphine stimulation to promote μOR internalization in enteric neurons. This study tested the effect of chronic treatment with fentanyl, a μOR internalizing agonist, on ligand-induced endocytosis and the expression of the intracellular trafficking proteins, dynamin and ß arrestin, in enteric neurons using organotypic cultures of the guinea pig ileum. In enteric neurons from guinea pigs chronically treated with fentanyl, μOR immunoreactivity was predominantly at the cell surface following acute exposure to morphine with a low level of μOR translocation, slightly higher than in neurons from naïve animals. This internalization was not due to morphine direct effect because it was also observed in neurons exposed to medium alone. By contrast, D-Ala2-N-Me-Phe4-Gly-ol5-enkephalin (DAMGO), a potent μOR-internalizing agonist, induced pronounced and rapid μOR endocytosis in enteric neurons from animals chronically treated with fentanyl or from naïve animals. Chronic fentanyl treatment did not alter dynamin or β-arrestin expression. These findings indicate that prolonged activation of μORs with an internalizing agonist such as fentanyl does not enhance the ability of acute morphine to trigger μOR endocytosis nor induces changes in intracellular trafficking proteins, as observed with prolonged activation of μORs with a poorly internalizing agonist such as morphine. Cellular adaptations induced by opiate chronic treatment might be ligand dependent and vary with the agonist efficiency to induce receptor internalization.
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