Safety, Tolerability, & Pharmacokinetics Study of Single & Multiple Inhaled Doses of Imatinib Inhalation Solution

This is a randomised, double-blind, placebo-controlled, dose escalation study to evaluate the safety, tolerability, and PK of single and multiple inhaled doses of imatinib inhalation solution (AER-901) in healthy adult volunteers. This study consists of 3 parts and an optional fourth part: * Part A: double-blind, placebo-controlled, single ascending dose (SAD). * Part B: double-blind, placebo-controlled, multiple ascending dose (MAD). * Part C (optional): open-label, single-dose, crossover. The decision to proceed with Part C will be made by the Sponsor after reviewing unblinded safety and PK data from Part D of the study. * Part D: double-blind, placebo-controlled, 5 mg single dose (SD) followed by a twice daily (BID) 5 mg dose (total daily dose of 10 mg) of AER-901 in a propylene glycol formulation vs. placebo. Oversight for the study will be provided by an SRC composed of the Principal Investigator (PI), the Sponsor's Medical Monitor (MM) and an independent MM. The decision to progress from Cohort A1 to Cohort A2 will be based on safety and tolerability data and not PK data from Cohort A1. However, the decision to progress from Cohort A2 to Cohort A3 will be based on review of safety and tolerability data from Cohort A2 and PK data from Cohort A1 by the SRC. A similar sequence will follow for subsequent progression decisions by the SRC for the cohorts in Part A and Part B of the study. All parts of the study (A, B, C, and D) will include a 28-day Screening period, a Treatment period, and a Follow-up period. Parts C and D include an additional treatment period and a Washout period between the 2 treatment periods. Throughout this Study Protocol, timings for post-dose assessments for spirometry, ECG, blood and urine samples for PK analysis are stated in relation to completion of the most recent dose of IP.