A Study to Investigate the Safety and Tolerability of Single and Repeat Doses of PC786

Inclusion Criteria: All subjects (Cohorts 1, 2, 3 \& 4) * Must be male or female, aged between 18 and 65 years inclusive (at the time of consent) who fit one of the following criteria: women of childbearing potential who are willing and able to use contraception from screening until 30 days after receipt of the final dose; Women of non-childbearing potential defined as being amenorrhoeic or have been permanently sterilised; Men who are willing and able to use contraception from the time of the first dose, until 90 days after receipt of the final dose of study medication. * Females must have a negative serum β human chorionic gonadotropin (β-hCG) test at screening and a negative urinary pregnancy test at Day -1. * Subject must be willing and able to adhere to the restrictions and prohibitions required by this protocol. * Each subject must sign an informed consent form (ICF) indicating that he or she understands the purpose and requirements of the study and that they are willing to participate. * Body weight ≥ 50 kg and body mass index (BMI) within the range 18 - 30 kg/m2 (inclusive). * Average QTcF \<450 msec at screening and pre-dose. * Vital signs assessments within normal ranges at screening and pre-dose. Healthy Subjects (Cohorts 1, 2 \& 3) * Healthy as determined by a physician based on a full medical examination including medical history, physical examination and laboratory tests performed at screening and pre-dose. * Spirometry readings (FEV1 and FVC) to be ≥ 80% of predicted value and FEV1/FVC ratio \> 0.7 at screening Subjects with Asthma (Cohort 4) * Documented diagnosis of asthma, first diagnosed at least 12 months prior to the screening visit. * Subject must demonstrate a PC20 methacholine ≤ 8 mg/mL at the screening visit. * Have an FEV1 \>60% of predicted normal value at least 6 h after the last use of a short acting β-agonist (SABA). * Have stable asthma based on physician assessment at screening and prior to randomisation * Subject must be otherwise healthy on the basis of a full medical examination including medical history, physical examination and laboratory tests performed at screening. Exclusion Criteria: All subjects (Cohorts 1, 2, 3 \& 4) * Any acute illness. * Upper or lower respiratory tract infection within 4 weeks of the screening visit or randomisation. * Use of prescription medications within 14 days of the Screening visit * Are taking over the counter medications other than vitamins or multivitamins and herbal medication, within 14 days prior to Screening * History of regular alcohol consumption within 6 months of the study of an average weekly intake of \>21 units for males, or \>14 units for females * Definite or suspected history of drug or alcohol abuse within the previous 5 years. * A smoker (regular or irregular), or has smoked or used nicotine-containing products (including e-cigarettes) within the 6 months prior to screening * A positive test for HIV-1 \& -2 antibodies at screening. * A positive pre-study hepatitis B surface antigen or positive hepatitis C antibody result at screening. * Positive test for alcohol, smoking or drugs of abuse, at screening or pre-dose * Received an experimental drug or used an experimental medical device within 3 months before the first dose of the study drug is scheduled. * Allergy to any of the active or inactive ingredients in the study medication. * History of drug, or other allergy that would contraindicate participation. * Donation of blood in excess of 500 mL within a 3 month period prior to dosing * Mentally or legally incapacitated. * An employee of the Sponsor or contract research organisation (CRO), or a relative of an employee of the Sponsor or CRO. * Unable or unwilling to undergo multiple venepuncture procedures * Pregnant or lactating female * Any other reason that the Investigator considers makes the subject unsuitable to participate. Healthy Subjects (Cohorts 1, 2 \& 3) * Any chronic illness or clinically relevant abnormality identified on the screening medical assessment, laboratory tests or ECG Subjects with Asthma (Cohort 4) * Has ever had an episode of life-threatening asthma defined as respiratory arrest, intubation for asthma, or ICU admission for asthma. * Presence of clinically significant diseases other than asthma, hyper-responsive airways, seasonal allergic rhinitis or atopic diseases * Has experienced an acute asthma exacerbation in the 12 months prior to screening requiring hospitalisation or accident and emergency treatment or management with systemic or injectable steroids. * Has uncontrolled, or moderate to severe asthma based on PI assessment and/or use of prohibited medications, or has required treatment with these therapies in the previous 12 weeks. * History or presence of any known conditions contraindicated for methacholine challenge