A Phase I Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of TPN171H, a Novel Phosphodiesterase Type 5 Inhibitor, in Healthy Subjects

Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs

Pulmonary arterial hypertension (PAH) is a malignant pulmonary vascular syndrome characterized by a progressive increase in pulmonary vascular resistance and pulmonary arterial pressure, which eventually leads to right heart failure and even death. Although the exact mechanism of PAH is not fully understood, pulmonary vasoconstriction, vascular remodeling, immune and inflammatory responses, and thrombosis are thought to be involved in the development and progression of PAH. In the era of non-targeted agents, PAH had a very dismal prognosis with a median survival time of only 2.8 years. With the deep understanding of the pathophysiological mechanism of PAH as well as advances in drug research, PAH-specific therapeutic drugs have developed rapidly in the past 30 years, but they primarily focus on the three classical signaling pathways, namely the endothelin pathway, nitric oxide pathway, and prostacyclin pathway. These drugs dramatically improved pulmonary hemodynamics, cardiac function, exercise tolerance, quality of life, and prognosis in PAH patients, but could only reduce pulmonary arterial pressure and right ventricular afterload to a limited extent. Current targeted agents delay the progression of PAH but cannot fundamentally reverse pulmonary vascular remodeling. Through unremitting efforts, new therapeutic drugs such as sotatercept have emerged, injecting new vitality into this field. This review comprehensively summarizes the general treatments for PAH, including inotropes and vasopressors, diuretics, anticoagulants, general vasodilators, and anemia management. Additionally, this review elaborates the pharmacological properties and recent research progress of twelve specific drugs targeting three classical signaling pathways, as well as dual-, sequential triple-, and initial triple-therapy strategies based on the aforementioned targeted agents. More crucially, the search for novel therapeutic targets for PAH has never stopped, with great progress in recent years, and this review outlines the potential PAH therapeutic agents currently in the exploratory stage to provide new directions for the treatment of PAH and improve the long-term prognosis of PAH patients.

Pharmacokinetics, mass balance, and metabolism of [14C]TPN171, a novel PDE5 inhibitor, in humans for the treatment of pulmonary arterial hypertension

TPN171 is a novel phosphodiesterase-5 (PDE5) inhibitor used to treat pulmonary arterial hypertension (PAH) and erectile dysfunction (ED), which currently is undergoing phase II clinical trials in China. In this single-center, single-dose, nonrandomized, and open design study, radiolabeled [¹⁴C]TPN171 was used to investigate the metabolic mechanism, pharmacokinetic characteristics, and clearance pathways of TPN171 in 6 healthy Chinese male volunteers. Each volunteer was administered a single oral suspension of 10 mg (100 μCi) of [¹⁴C]TPN171. We found that TPN171 was absorbed rapidly in humans with a peak time (T_max) of 0.667 h and a half-life (t_1/2) of approximately 9.89 h in plasma. Excretion of radiopharmaceutical-related components was collected 216 h after administration, accounting for 95.21% of the dose (46.61% in urine and 48.60% in feces). TPN171 underwent extensive metabolism in humans. Twenty-two metabolites were detected in human plasma, urine, and feces using a radioactive detector combined with a high-resolution mass spectrometer. According to radiochromatograms, a glucuronide metabolite of O-dealkylated TPN171 exceeded 10% of the total drug-related components in human plasma. However, according to the Food and Drug Administration (FDA) guidelines, no further tests are needed to evaluate the safety of this metabolite because it is a phase II metabolite, but the compound is still worthy of attention. The main metabolic biotransformation of TPN171 was mono-oxidation (hydroxylation and N-oxidation), dehydrogenation, N-dealkylation, O-dealkylation, amide hydrolysis, glucuronidation, and acetylation. Cytochrome P450 3A4 (CYP3A4) mainly catalyzed the formation of metabolites, and CYP2E1 and CYP2D6 were involved in the oxidative metabolism of TPN171 to a lesser extent. According to the incubation data, M1 was mainly metabolized to M1G by UDP-glucuronosyltransferase 1A9 (UGT1A9), followed by UGT1A7 and UGT1A10.