Safety, Tolerability, and PK Parameters of Sodium Nitrite Inhalation Solution in Healthy Subjects

Pulmonary hypertension (PH) is an increase in the blood pressure (BP) in the small pulmonary vessels, arteries, veins or capillaries that results in progressive increases in right ventricular afterload, often leading to right ventricular failure and death. Pulmonary hypertension can result from a multitude of pathologies, including arterial etiologies, venous, chronic hypoxia related, thromboembolic, and other miscellaneous etiologies. In the recent Dana Point Classification, pulmonary arterial hypertension (PAH) was classified as Group 1. In Group 1 PAH, the pathologic lesion is localized to the small muscular pulmonary arteries, resulting in luminal narrowing and resistance to blood flow. Group 1 PAH includes idiopathic or sporadic PAH and heritable PAH which includes those with a family history of PAH. Associated PAH includes disease associated with connective tissue disease as well as PAH associated with congenital systemic to pulmonary shunts, portal hypertension, and human immunodeficiency virus (HIV) infection. Drug and toxin induced PAH is also in Group 1. Untreated, patients with PAH have an average life expectancy of 3 years, which declines to approximately 1 year if right heart failure is present. Inhaled nitric oxide (NO) is a potent acute vasodilator. Its acute administration results in improved hemodynamics in the 10 to 15% of patients with PAH who demonstrate acute vasoreactivity. However, the usefulness of NO for chronic therapy is limited by the need for continuous inhalation. In patients who demonstrate vasoreactivity during an acute challenge with inhaled NO or a prostanoid challenge, therapy with calcium channel blockers has been demonstrated to result in improved symptoms and survival. In patients who do not demonstrate an acute vasodilator response, available therapies for PAH include prostanoids, endothelin receptor antagonists (ERA), and phosphodiesterase type-5 (PDE-5) inhibitors. However, the route and frequency of administration of the prostanoids, the hepatotoxicity of the ERAs, and concerns about the sustained efficacy of both the ERAs and PDE-5 inhibitors suggests that many patients with PAH could benefit from an effective therapy which offers ease of administration and a favorable toxicity profile. Aires Pharmaceuticals, Inc. is developing a novel therapeutic, AIR001, for the treatment of PAH. The active ingredient in AIR001 is sodium nitrite, formulated in a buffered, pH-adjusted solution for nebulization. Preclinical data suggest that under the hypoxic, acidotic conditions present in the pulmonary hypertensive lung, inhaled sodium nitrite serves as a sustained release source of NO which will act as an acute pulmonary vasodilator. In addition, because decreased levels of NO have been shown to stimulate vascular remodeling, the increased NO resulting from nitrite inhalation is postulated to attenuate or reverse the pulmonary arterial remodeling process, resulting in both symptomatic improvement and pulmonary hemodynamic improvement in patients with PAH. Preclinical experiments have shown that AIR001 by oral, IV, and inhalation routes of administration is effective in treating PAH induced by hypoxia or monocrotaline when administered as infrequently as once weekly at doses that generate plasma concentrations of approximately 1 to 10 uM and above. While the precise mechanism by which AIR001 exerts anti-hypertensive actions in PAH models remains to be elucidated, nitrite itself has been demonstrated to be metabolized to NO in animals and humans. Single doses of AIR001 have been shown to be well tolerated in humans at dose levels that generate peak plasma concentrations (Cmax) in the target range established in preclinical models and no safety issues have been identified. AIR001 reduced PH induced by hypoxic gas inhalation in healthy volunteers at doses that are well tolerated. Preclinical and clinical data support further clinical investigation of inhaled AIR001 for the treatment of PAH. Before progressing to studies in patients with PAH, the safety and tolerability of multiple dose administration of AIR001 will be evaluated in Part A of the current study. The PDE-5 inhibitor, sildenafil, is approved for use in patients with PAH and commonly used in the initial treatment for PAH. AIR001 is converted to NO, which increases cGMP dependent vasodilatation. Because PDE-5 inhibitors prevent the catabolism of cGMP by phosphodiesterase, it is possible that an exaggerated drug effect could be observed when AIR001 is administered to patients being treated with sildenafil. Therefore, combination safety and tolerability (in particular orthostatic effects) of escalating single doses of AIR001 will also be evaluated in combination with steady-state sildenafil in Part B of the study. A cohort of patients with previously diagnosed PAH on stable background therapy will be assessed for safety and tolerability of multiple doses of AIR001 in Part C of the study. Part D of the study will assess the PK, safety and tolerability of single dose AIR001 with each of three different nebulizers in a randomized crossover design.